Field data collected in cross-sections of tide-dominated estuaries reveal that flow and suspended sedimentconcentration show pronounced spatial and temporal behavior, which depend on factors like tidal discharge,density gradients and the geometry of the cross-section. Models are capable of reproducing and explainingmany aspects of the observations, but also marked discrepancies occur between model results and data. Theobjective of the present study is to systematically investigate the sensitivity of model output to formulationsof physical processes. This is done by comparing two types of models. The first is a numerical model (NM)that solves the full shallow water equations with prognostic salt dynamics. The second is an IM that solves areduced set of equations for tidal water motion and uses a diagnostic salinity field. The IM can be used as atool to interpret the complex output of the NM. The NM, on the other hand, can be used to probe the limits ofapplicability of the IM and may give hints on further improvements of the IM.